Arenas have been very popular since their release, and today Drysc had the following to say about releasing additional arenas.

We're definitely going to be adding more as we go, and probably sooner rather than later. Of course we'll give you a big shiny page with details when we're ready to announce something.

We also aren't abandoning the battleground system by any stretch of the imagination. We have some pretty cool ideas in the works, but nothing we can discuss just yet. You'll have to be patient. Enjoy Eeyots, the arenas, and we'll talk later.